Fact of Pneumocystis Jiroveci

Some Key points regarding Pneumocystis Jiroveci

1. Previously it was called Pneumocystis carinii
2. Thought to be a protozoan.  Presently it is believed to be a fungus.
3. But antifungal drugs are ineffective
4. P. jiroveci is the only Pneumocystis species that infects humans,
5. Pneumocystis jiroveci is common in the environment and does not cause illness in healthy people.
   1. Organism of low virulence
   2. Most 5 years old children in USA has antibodies to this organism
   3. Asymptomatic infection quiet common
   4. Pneumocystis jiroveci was a relatively rare infection before the AIDS epidemic

Similarities of Pneumocystis Jiroveci with protozoa

1. In tissue it appears as cyst: That resemble the cyst of Protozoa.
2. Does not grow in vitro in fungal culture media
3. Requires tissue culture/cell lines for its growth and viability.
4. Absence of ergosterol in cytoplasmsic membrance: insensitive to antifungal drugs
5. Susceptible to selected anti-protozoan agents

Pneumocystis Jiroveci is considered as fungi because

1. Pneumocystis takes fungal stain eg. Methenamine silver stain
2. Possess chitin in all stages of its life cycle
3. The protein synthesis elongation factor (EF3) and thymidylate synthase of Pneumocystis are more homologous to those of ascomycetous fungi
4. Pneumocystis and fungi have similar cyst wall ultrastructure
5. The ribosomal RNA studies reveal that 16S like RNA of Pneumocystis shares substantial sequence homology with various species of Ascomycota

Some points regarding pathogenesis of Pneumocystis Jiroveci

1.  Extracellular pathogen
2. Transmission occurs by inhalation.
3. Escape the defence of upper respiratory tract
4. Deposition in alveoli
5. Trophozoites attach to alveolar epithelium (alveolar type I epithelial cells) and proliferate
6. Alevolar type II cell hypertrophy: Macrophage infiltrate and filling of alveolar spaces with foamy eosinophilic material and plasma cells.
   1. Plasma cell pneumonia
7. Foci of necrosis and cellular debris in extrapulmonary sites.